Summary
Behavioral tests for pigs before weaning currently have limited evidence supporting their ability to predict aggressive or non-aggressive biting behaviors from post-weaning into adulthood. According to this article, pigs typically engage in aggressive biting during fights for dominance and competition for resources. Conversely, pigs are non-aggressive when they are able to satisfy their behavioral needs, such as foraging and rooting. There is a slight relationship between low resisting pigs (i.e. pigs deemed to be passive during behavioral tests) engaging in non-aggressive biting and high resisting pigs engaging in aggressive biting. However these behavioral tests are not yet considered a reliable and valid predictor of biting behavior. Other factors also predict biting behaviors. When a pregnant pig experiences higher stress and poorer nutrition, her offspring can have cognitive issues leading to a proneness to bite. Socialization of the piglets can also lead to reduced biting; however, more research is needed. Environmental factors and enrichment have been promising in reducing biting behavior as some studies conclusively show an enriching and familiar environment reduces tail biting. Other factors reviewed include fetal nutrition, postnatal stress, nutrition, competition, and age of weaning. However, none of these factors have enough evidence to suggest they can accurately predict biting behavior in adulthood. Overall this review illustrates the need for more research examining the biting behavior of pigs.
The pig industry faces many animal welfare issues. Among these, biting behaviour has a high incidence. It is indicative of an existing problem in biters and is a source of physical damage and psychological stress for the victims. We categorize this behaviour into aggressive and non-aggressive biting, the latter often being directed towards the tail. This review focusses specifically on predisposing factors in early life, comprising the prenatal and postnatal periods up to weaning, for the expression of aggressive and non-aggressive biting later in life. The influence of personality and coping style has been examined in a few studies. It varies according to these studies and, thus, further evaluation is needed. Regarding the effect of environmental factors, the number of scientific papers is low (less than five papers for most factors). No clear influence of prenatal factors has been identified to date. Aggressive biting is reduced by undernutrition, cross-fostering and socialization before weaning. Non-aggressive biting is increased by undernutrition, social stress due to competition and cross-fostering. These latter three factors are highly dependent on litter size at birth. The use of familiar odours may contribute to reducing biting when pigs are moved from one environment to another by alleviating the level of stress associated with novelty. Even though the current environment in which pigs are expressing biting behaviours is of major importance, the pre-weaning environment should be optimized to reduce the likelihood of this problem.